1. Field of the Invention
The present invention relates to the art of axle/suspension systems for vehicles. More particularly, the invention relates to the art of trailing and leading arm air-ride axle/suspension systems for heavy-duty vehicles, such as tractor-trailers or semi-trailers, which cushion the vehicle ride for occupants and cargo and stabilize the vehicle during operation.
2. Background Art
Heavy-duty vehicles, such as tractor-trailers or semi-trailers and dump trucks, typically include one or more leading or trailing arm air-ride suspension systems that connect the frame of the vehicle to the wheel-bearing axles of the vehicle. Each pair of leading or trailing arm suspension assemblies that are connected to a respective axle is known in the art as an axle/suspension system and acts to cushion the ride and stabilize the vehicle. That is, as the vehicle is traveling over-the-road, its wheels encounter road conditions that impart various forces, loads and/or stresses, collectively referred to herein as forces, to the respective axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. In order to minimize the detrimental effect of these forces on the vehicle as it is operating, the axle/suspension system is designed to absorb at least some of them.
These forces include vertical forces caused by vertical movement of the wheels as they encounter certain road conditions, fore-aft forces caused by acceleration and deceleration of the vehicle, and side-load and roll forces associated with transverse vehicle movement, such as turning of the vehicle and lane-change maneuvers. In order to absorb such disparate forces, axle/suspension systems have differing structural requirements. More particularly, a dampening of vertical forces leads to a desire to have an axle/suspension system structure that is relatively flexible. In contrast, fore-aft forces and roll forces lead to a desire to have an axle/suspension system that is fairly rigid to minimize the amount of sway experienced by the vehicle and thus provide stability. Moreover, the rigidity of an axle/suspension system must be offset or tempered by some degree of roll compliance to prevent failure of components in the system.
In the prior art, these competing demands have led to air-ride axle/suspension systems with many separate components. While such prior art systems include shock absorbers and air springs to dampen vertical movement of the vehicle, many other components are necessary. For example, hangers are attached to the vehicle frame, leading or trailing arm beams ate pivotally connected to the hangers at one beam end and are welded to the axle at the other beam end. Rubber pivot bushings that are softer in the vertical direction than in the fore-aft horizontal direction are typically used to connect the leading or trailing arm beams to the hangers. These bushings, known in the art as TRI-FUNCTIONAL® bushings, which is a registered trademark owned by Hendrickson USA, L.L.C., the assignee of the present invention, exhibit compliance so that a certain degree of roll can be maintained, while the other components of the system remain relatively rigid and non-compliant.
Other prior art axle/suspension systems include components such as trailing arm beam weldments that are bolted onto axle seats with a pair of pins. Rubber bushings are used in the axle seats and in pivot joints that connect the trailing arms to the vehicle frame to provide roll compliance. Still other axle/suspension systems include trailing arm beams that are stiff leaf springs, which rigidly attach to the axle and pivotally mount with bushing assemblies to the vehicle frame. The leaf springs provide roll compliance for these systems.
The integral nature of the axle in these prior art axle/suspension systems requires it to function as a large anti-roll bar, vertical and fore-aft beaming structure, and side load support structure. Such a concentration of forces on the axle increases the chance of failure of the rigid connection between leading or trailing suspension beams and the axle, as well as of the axle itself In addition, the use of multiple specialized components in these prior art axle/suspension systems leads to a significant amount of expense involved in the time, labor, and equipment needed to manufacture and assemble the system Moreover, these additional components add to the complexity of the axle/suspension system, increasing the possibility of failure of joined components and creating the possibility of their frequent repair or replacement. Furthermore, the use of limited flexible components in the prior art, such as bushings, isolates certain forces in the bushings, which may create stress risers in them that decrease their useful life.
As a result, a need has existed in the art to develop an axle/suspension system that overcomes the disadvantages of the prior art and provides an axle/suspension system that has an improved structure, is lighter in weight and, as a result, distributes forces using fewer components. These disadvantages are overcome by the present invention through the use of an integral arm axle/suspension system that distributes forces and eliminates the hangers, bushings, and conventional leading or trailing arm beams, as well as the axle tube of prior art axle/suspension systems in certain embodiments.